The difference wasn't so pronounced before. Doom/Doom2 were certainly 'playable technology demos' but their game play was still *really* good.
Doom rolled in at a time when all other titles were using the Wolfenstein engine and had an aproach that was heavy on game design. There was a lot of emphasis on creative solutions to make 3-d games seem innovative without spending much on technology or art.
Blake Stone had NPC scientists you had to talk to (way before Half-life), it had monsters interacting with vending machines (and vending machines you could use to regen life).
Corridor 7 Featured a random creepy Hallucination and had different types of vision (for night and for invisible monsters) and it even featured some pretty innovative shapeshifting monsters.
Doom had an emphasis on engine and art that just wasn't around at the time. Doom was not design heavy (in fact they fired their game designer at early stages of development). By the time Quake was around, being all around the same damn game as Doom, players were just not that impressed by the true 3d engine, prefering games like Duke Nukem 3d, which had a heavy emphasis on design and gameplay.
Somewhat recently, id again went for another technology heavy game with Doom3, but this time trying to learn from their past mistakes, by making it heavy on scripted events (because Half-Life did it). The result was a gameplay disaster that no one plays without the flashlight mod. If the game had stayed closer to the original Doom, all would had been forgiven (as it would had been a refreshing blast from the past).
It is also not much of a stretch, but would had anyone complained if Duke Nukem Forever had a much more dated engine (and thus a much lower price):
...if released 8 years ago, perhaps some of the dated jokes would have at least raised a smile
Why every FPS out there looks so dirty and pesimistic and features a sort of apocalypse? Do FPS designers need a hug?, what ever happened to adding a few colors to the experience? Even if this means they would have to make their games in a dated engine, it could be welcomed (there are more locations than the same besieged and runned down ship, city or planet).